Tensioner

Abstract

A tensioner for traction means such as a belt, includes a housing which accommodates a cylinder for guiding a hydraulically dampened, spring-loaded plunger in an axial direction for tensioning the traction means. The interior space of the housing is closed by a cover which has a guide opening for passage of the plunger. A seal is placed outside the cover to seal an annular opening bounded by the housing and the plunger. In order to prevent a gas cushion under pressure and trapped between the cover and the seal, from pushing the seal from its seat, the cover is formed with a vent passageway which communicates with the interior space for release of the gas cushion via the vent passageway into the interior space.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:  
     
       1. A tensioner, comprising: 
       a housing defining an axis and having an interior space;  
       a cylinder received in the interior space of the housing;  
       a hydraulically dampened, spring-loaded plunger guided in the cylinder for displacement in an axial direction and tensioning of a traction member;  
       a cover closing the interior space of the housing and having a guide opening for passage of the plunger; and  
       a seal mounted outside of the cover onto the plunger and destined to seal an annular opening bounded by the housing and the plunger,  
       said cover being formed with a vent passageway in communication with the interior space for release of a gas cushion, forming between the seal and the cover, via the vent passageway into the interior space,  
       wherein the housing is formed with a radial shoulder for support of the cover, said vent passageway of the cover being so sized as to overlie said radial shoulder and to project radially inwards beyond the radial shoulder.  
     
     
       2. The tensioner of claim  1  wherein the housing has a cylindrical receptacle so as to define a seat for the cover and for the seal, said cover and said seal each having an outer peripheral surface bearing upon an inside wall surface of the cylindrical receptacle. 
     
     
       3. The tensioner of claim  1  wherein the cover has an outer circumference, said vent passageway being formed by bores provided about the outer circumference of the cover. 
     
     
       4. The tensioner of claim  1  wherein the plunger is spring-loaded by a helical compression spring having one end resting on a housing bottom and another end bearing against a spring plate mounted on the plunger and impacting the cover at an impact zone when the plunger is moved out of the cylinder, with the vent passageway having an cross sectional area which is so positioned as to communicate with the interior space at least partially outside the impact zone.